The present invention relates to a video camera most suitable for use of such as a CCD camera, and more particularly to a video camera having a front panel, on which a lens mount is formed, and an imaging device such as a CCD is spaced at an adjustable distance from the lens mount along an optical axis.
A CCD camera as an example of the video camera has already been proposed by the present applicant as disclosed in Japanese Patent Application No. Hei5-258848, for example. FIGS. 51 to 53 show such a CCD camera 1 in the related art. The exterior of the CCD camera 1 is composed of three separate parts, i.e., a front panel 2, a camera case 3, and a rear panel 4. The front panel 2 is formed by die casting such as aluminum die casting, or it is composed of a front panel chassis 2A formed by die casting and a front panel cover 2B formed by molding of a synthetic resin or the like for covering the front panel chassis 2A. The camera case 3 is composed of an upper case and a lower case each formed from a sheet metal or the like. The rear panel 4 is composed of a rear panel chassis formed from a sheet metal or the like and a rear panel cover formed as a molded part for covering the rear panel chassis. The front panel 2 has a front wall 2a formed with an annular lens mount 5 perpendicular to an optical axis P as surrounding the optical axis P. The annular lens mount 5 is formed over its inner circumference with a lens mounting portion 6 such as a tapped hole. Although not shown, a lens such as a C-mount lens and a CS-mount lens is removably mounted to the lens mount 5.
Installed inside the front panel 2 of the CCD camera 1 is a flange back focus adjusting mechanism 11 for adjusting a flange back focus of a CCD 12 as an imaging device with respect to the lens mount 5 according to the kind of the lenses (e.g., a C-mount lens and a CS-mount lens) removably mounted to the lens mount 5. The flange back focus adjusting mechanism 11 includes the CCD 12, a substantially circular CCD holder 13 formed of a synthetic resin as an imaging device holder, a circular adjuster ring 14 formed of a synthetic resin, a pair of cam followers 15 formed on the outer circumference of the CCD holder 13 so as to be circumferentially equally spaced at 180xc2x0 from each other, a pair of arcuate cams 16 formed on the inner circumference of the adjuster ring 14 so as to be circumferentially equally spaced at 180xc2x0 from each other and to face the cam followers 15 in the direction shown by an arrow a, a pair of compression springs 17 as means for pressing the cam followers 15 onto the cams 16 in the direction shown by an arrow b opposite to the arrow a, a ring holder plate 18 as a ring holding member formed from a sheet metal or the like for holding the adjuster ring 14 from its rear side in the direction of the arrow a, and a lock member 19 for locking the adjuster ring 14. The CCD 12 is preliminarily mounted in the CCD holder 13 together with a filter bracket 20, a filter 21, a rubber seal 22, a CCD bracket 23, and a CCD board 24 in perpendicular relationship with the optical axis P.
The front panel 2 has a rear wall 2b from which a cylindrical portion 25 projects parallel to the optical axis P in the direction of the arrow b. The flange back focus adjusting mechanism 11 is assembled by first mounting the springs 17, the CCD holder 13, the adjuster ring 14, the ring holder plate 18, and the lock member 19 in this order in the direction of the arrow a into the front panel 2 at inner and outer circumferential portions of the cylindrical portion 25, and then fastening the ring holder plate 18 at its four corners to the rear wall 2b of the front panel 2 by means of four screws 26 against the biasing forces of a pair of springs 17. The lock member 19 is mounted between the adjuster ring 14 and a side wall 2c of the front panel 2, and is releasably pressed on the adjuster ring 14 by a set screw 27 laterally screwed through the side wall 2c in a direction perpendicular to the optical axis P.
The front panel 2 has upper and lower walls 2d formed with a pair of upper and lower slits 28 in cooperation with upper and lower recesses of the camera case 3, and the adjuster ring 14 is exposed at its upper and lower portions through the upper and lower slits 28. Accordingly, by rotating the adjuster ring 14 at these exposed portions, a pair cams 16 operate to axially move the cam followers 15 in the directions of the arrows a and b along the optical axis P in cooperation with the springs 17, thereby adjusting the flange back focus of the CCD 12 with respect to the lens mount 5. As shown in FIG. 52, connectors 31, terminal strips 32, switches 33, and a volume controller 34 are mounted on the rear panel 4.
As shown in FIGS. 49A and 49B and FIGS. 50A and 50B showing the cam mechanism of the CCD camera 1 in the related art, each of the pair of cam followers 15 of the CCD holder 13 is integrally formed with two radially extending ribs 15c having different height H1 and H2 in the direction of the optical axis P. The two ribs 15c of each cam follower 15 are kept in pressure contact with three tilted cam surfaces 16a, 16b, and 16c of the corresponding cam 16 by the corresponding spring 17 in the direction of the optical axis P. The three tilted cam surfaces 16a, 16b, and 16c are different in angle of tilt and height in the direction of the optical axis P.
Accordingly, the flange back focus adjusting mechanism 11 in the related art CCD camera 1 is designed so as to maintain the balance of the CCD holder 13 in a four-point contact fashion such that the total four ribs 15c of the pair of cam followers 15 equally spaced at 180xc2x0 from each other in the circumferential direction of the CCD holder 13 are in contact with the cam surfaces 16a, 16b, and 16c of the pair of cams 16 spaced at 180xc2x0 from each other in the circumferential direction of the adjuster ring 14. However, in actual, the four ribs 15c are not always in contact with the cam surfaces 16a to 16c, but three of the four ribs 15c variably come into contact with the cam surfaces 16a to 16c. In other words, any one of the four ribs 15c is always separate from the cam surfaces 16a to 16c. Accordingly, the CCD holder 13 is minutely vibrated depending on what ribs 15c are used to keep the balance of the CCD holder 13.
The cam surfaces 16a and 16b are formed in gentler slopes for fine adjustment, and the cam surface 16c is a steep slope for coarse adjustment, therefore, the angle of tilt thereof differs from each other. Further, the heights H1 and H2 of the two ribs 15c of each cam follower 15 are set so as to correspond to the angle of tilt of the gentle cam surfaces 16a and 16b. Accordingly, the two ribs 15c are stable on the gentle cam surfaces 16a and 16b, but are not stable on the steep cam surface 16c. Furthermore, when a point 16d between the cam surfaces 16a and 16c or another point 16d between the cam surfaces 16c and 16b comes between the two ribs 15c as shown in FIG. 50B, undue tilt forces are applied to the two cam followers 15, causing an unstable holding condition of the CCD holder 13. The instability of the CCD holder 13 causing vibrations is a serious problem because it immediately causes face vibrations of the CCD 12, which lead to a deterioration in image quality.
It is accordingly an object of the present invention to provide a video camera which can always stably perform adjustment of the flange back focus of the imaging device.
According to an aspect of the present invention, there is provided in a video camera having a front panel, on which a lens mount is formed and an imaging device thereof is spaced at an adjustable distance from the lens mount along an optical axis, the improvement comprising an adjuster ring provided inside of the front panel so as to be rotatable about the optical axis, for adjusting the adjustable distance, the adjuster ring being formed with three arcuate cams circumferentially equally spaced from each other, an imaging device holder for holding the imaging device, the imaging device holder being formed with three cam followers circumferentially equally spaced from each other, and means for respectively pressing the three cam followers of the imaging device holder onto the three arcuate cams of the adjuster ring along the optical axis.
With this configuration, the cam followers of the imaging device holder can always be kept in pressure contact with the cams of the adjuster ring at three points by the pressing means, so that the balance of the imaging device holder can be maintained always stably. That is, the cam followers of the imaging device holder are always kept in contact with the cams of the adjuster ring at three points to thereby maintain the balance of the imaging device holder always stably. Accordingly, the imaging device held in the imaging device holder can always be balanced to thereby provide an always stable image without face vibrations or the like, thus improving the reliability of the video camera.
According to another aspect of the present invention, there is provided in a video camera having a front panel, on which a lens mount is formed and an imaging device is spaced at an adjustable distance from the lens mount along an optical axis, the improvement comprising a cylindrical portion formed inside of the front panel so as to extend coaxially with the optical axis, the cylindrical portion being formed with three guide slots circumferentially equally spaced from each other and extending parallel to the optical axis, an adjuster ring rotatably mounted on the outer circumference of the cylindrical portion for adjusting the adjustable distance, three arcuate cams formed at the outer circumference of the cylindrical portion on one side surface of the adjuster ring opposed to the front panel and circumferentially equally spaced from each other, the three arcuate cams being rotatable on the outer circumference of the cylindrical portion about the optical axis, an imaging device holder for holding the imaging device, the imaging device holder being inserted in the cylindrical portion so as to be movable along the optical axis, three cam followers formed on the outer circumference of the imaging device holder and respectively inserted in the three guide slots of the cylindrical portion so as to be movable along the optical axis, the cam followers also serve for receiving springs, and three springs interposed between the front panel and the three cam followers of the imaging device holder for respectively pressing the three cam followers on the three arcuate cams of the adjuster ring along the optical axis.
With this arrangement, the three cam followers formed on the outer circumference of the imaging device holder are inserted in the three guide slots of the cylindrical portion of the front panel, and the three arcuate cams of the adjuster ring are fitted with the outer circumference of the cylindrical portion. The three cam followers of the imaging device holder are kept in pressure contact with the three cams of the adjuster ring by the three springs, respectively. Accordingly, the three cam followers can be stably pressed on the three cams by the three springs at three points, thereby maintaining the balance of the imaging device always stably.
Preferably, each of the three cam followers comprises a spring seat extending radially from the outer circumference of the imaging device holder in perpendicular relationship with the optical axis for receiving one end of the corresponding spring, a spring retainer formed on one side surface of the spring seat at a substantially central portion thereof for engaging the one end of the corresponding spring, and a single cam following rib formed on the other side surface of the spring seat at a substantially central portion thereof so as to extend radially for making contact with the corresponding arcuate cam.
With this arrangement, each cam follower includes the spring seat, the spring retainer, and the single cam following rib. Accordingly, the biasing force of each spring can be stably transmitted to the cam following rib of the corresponding cam follower, so that the imaging device holder can stably be pressed onto the three cams at the respective three cam following ribs. Moreover, each cam follower can smoothly follow the corresponding cam at its all portions including a gentler cam surface, a steep cam surface, and a change point therebetween, thereby stably maintaining the balance of the imaging device.